Various printing technologies have been extensively employed to form graphical elements on various substrates. For example, some printing methods (e.g. ink-jet printing) print various graphical elements by directing image forming fluids towards a printable surface. Some printing methods utilize transfer surfaces to apply colorants to a printable surface to form a graphical element thereon. The printable surface can form part of a printed substrate (e.g. paper or polymeric film) or can form part of an intermediate component adapted to transfer the colorant from the printable surface to the printed substrate (e.g. a blanket cylinder on a press). In either case, a colorant pattern is transferred to the printed substrate to form an image thereon. Various media including printing elements such as printing plates, printing sleeves, printing cylinders and the like include transfer surfaces. Transfer surfaces are used in various printing processes which can include, but are not limited to, offset, waterless offset, flexographic, gravure processes, or variations thereof.
The ability of these and other printing techniques to produce relatively low cost graphical images has lead to considerable interest in the field of printable electronics. This interest is particularly relevant in electronics, display and energy industries which require the formation of various patterns of conductive, semi-conductive and/or dielectric materials to form various functional entities including electronic circuits. The functional entities can include conductors, resistors, inductors, capacitors, rectifiers, transistors, opto-electronic devices, microwave devices, or acoustical devices by way of non-limiting example. Printing techniques are being considered to address the various needs of these industries. For example, some printing techniques have the potential to address the relatively large size requirements and low cost demands of various photovoltaic power assemblies. Additionally, various printing techniques are considered well suited for transferring patterns to flexible substrates which increases their potential for use in flexible display applications.
There is also a demand to combine printed graphical images with printed electronics. For example, there is a desire to replace bar-codes in packaging applications with more readily readable RFIDs. There is desire to create “smart packaging” and “smart publications” that can enhance the functionality provided between these articles and the customer. Mechanical, chemical, electrical or electronically-driven functions can enhance the desirability, usability or effectiveness of these articles in some way. Examples can include time or temperature sensitive food quality labels, self-heating or self-cooling containers for beverages and foods, or articles with electronic displays displaying select information based on a particular customer's desire. Accordingly, there is a desire that these articles be formed with printing techniques that can print in addition to various graphical elements, electronic circuits comprising various passive and active components including conductors, resistors, inductors, capacitors, transistors, displays, sensors, batteries, microphones, and the like.
Typically, some media undergo various processes to render their transfer surfaces in a suitable configuration for use in a printing process. These processes can include various image forming processes. For example, exposure processes are used to form images on a surface of media that has been suitably treated so as to be sensitive to light or heat radiation. One type of exposure-based image forming process employs film masks. Specialized recording apparatus can also be employed to directly form images on a surface of the media.
Image forming processes can include various scanning techniques to form various sub-images that are combined to form a desired image. For example, scanning can include establishing relative movement between a recording head and media as the recording channels of the recording head are activated to form corresponding image pixels on the media. A raster line or image pixel column comprising a series of image pixels is formed along a scan direction by a given recording channel as relative movement between the given recording channel and the media is established. Relative movement can include moving one or both of the recording channels and the media. The various raster lines of image pixels combine to form an image swath. In this manner various image portions are formed in corresponding image swaths. In some cases, scanning can be performed while deflecting radiation beams emitted by recording channels relative to media. In some cases, scanning can be performed while deflecting image forming material emitted by recording channels relative to media.
Recording apparatus known as computer-to-plate systems have been developed to form images on media. These recording apparatus can include various configurations including external drum, internal drum, and flat-bed configurations. The names of these different configurations typically refer to a configuration of a media support onto which media is positioned while forming images thereon. For example, an external drum recording system includes a cylindrical or drum-like media support onto which media is positioned while forming images thereon. Images are typically formed as the drum rotates about a rotation axis along a circumferential or main-scan direction while a recording head is moved along a sub-scan direction which is generally parallel to the rotation axis. Images are typically formed on the media by helical scanning techniques in which the movement of both the drum and the recording head are controlled to cause imaging beams emitted by the recording head to be scanned over the media along a spiral or helical path. Various external drum recording systems employing helical scanning techniques are examples of skewed recording systems. Skewed recording systems typically scan along a direction that is skewed relative to a desired orientation of an image to be formed during the scanning.
Various image distortions can arise when skewed recording systems are employed to form images. For example, in various external drum recording systems, helical scans are oriented from the main-scan axis by a skew angle determined by the movement of the recording head along the sub-scan axis during each revolution of the drum. Consequently, desired orthogonality characteristics of a rectangular shaped image can be adversely impacted as helical scanning causes the formed image to take a parallelogram shape.
Various techniques have been employed in the art to correct for orthogonality distortions. For example, U.S. Pat. No. 6,081,316 (Okamura et al.) describes a technique to correct for distortions caused by helical scanning in which image data is pre-distorted to compensate for the skewed imaging. In particular, an array of image data is shifted in a memory in an opposite direction to the helical scans to arrange the image data into an array having an “oppositely inclined” parallelogram structure. This pre-distorted image data compensates for the helical scanning to produce an image that substantially maintains the desired orthogonality requirements. Other orthogonality correction techniques include reading out image data along a read path running through the image data file at an angle corresponding to the helical scan angle. Orthogonality correction techniques are taught in U.S. Pat. No. 7,330,202 (Schweger et al.) and in European Patent Application 1 211 882.
FIGS. 1A and 1B show various conventionally formed skewed image swaths comparing imaged features which have selectively undergone orthogonality correction during their formation. In particular, FIG. 1A shows a typical helically formed image swath (i.e. helical image swath 100A) formed while not employing orthogonality correction techniques while FIG. 1B shows a typical helically formed image swath (i.e. helical image swath 100B) that is formed while employing a conventional orthogonality technique. Both helical image swaths 100A and 100B are shown skewed with respect to main-scan axis MSA by a helical scan angle θ. For clarity, both helical image swaths 100A and 100B are shown in an unwound or “flat” orientation. It is understood that each of helical image swaths 100A and 100B would helically wrap around the media support if formed in an external drum recording apparatus. Helical image swath 100A includes an image feature 47A that extends along the length of the swath. Although it is desired that image feature 47A extend along a direction that is parallel to a main-scan axis MSA, helical scanning techniques cause image feature 47A to assume a skewed orientation with respect to main-scan axis MSA. This skewed orientation is corrected in FIG. 1B. In this case, although helical image swath 100B is also shown in a skewed orientation with main-scan axis MSA (i.e. in the same orientation as helical image swath 100A), the employed orthogonality correction technique caused image feature 47B to be formed with a desired orientation (i.e. shown as a broken line 13) that is substantially parallel to main-scan axis MSA.
Analysis of FIG. 1B shows that one effect of the employed orthogonality correction technique is that image feature 47B is formed from a plurality of image feature portions 48 (i.e. image feature portions 48B in this case) that are arranged in a “stair-case” fashion. In this case, portions of image data have been read out along various skewed read paths that correspond to helical scan angle θ. The image data in each of the skewed read paths results in stair-case appearance of image feature 47B.
In many graphics-based applications, stair-cased image feature 47B would typically be perceived by the unaided human eye to appear to extend along direction of broken line 13 essentially in an un-interrupted fashion thereby rendering the employed orthogonality correction technique acceptable. There are exceptions however where stair-case image feature 47B would be noticeable to the un-aided human eye and would be considered objectionable. For example, in some lenticular applications, visible artifacts may be visible at the boundaries of the lenticular lenses. In some cases the lenticular lenses act as magnifying elements that make the stair-case effect more pronounced. In some applications, the formation of various security features (e.g. security strips) on various documents including currency would not be acceptable if these security features were formed with a staircase arrangement of image feature portions.
The functionality of the various printed electronic elements is of paramount importance in the field of printed electronics. Deviations in the conductive, dielectric or semi-conductive properties of the printed electronic elements can adversely impact the functionality of the electronics that they are incorporated into. For example, if image feature 47B corresponds to a printed conductive trace, very high areas of electrical resistance would be encountered at various stair-case shifts points associated with the employed orthogonality correction technique. This problem becomes especially pronounced as the demand for thinner conductors on the order of one or two pixels wide increases. Other electronic elements corresponding to orthogonality corrected image features similar to image feature 47B can suffer from similar problems.
There is a desire for improved image forming techniques that can combine various scanning techniques to improve image forming throughput while lessening image distortions.
There is a desire for improved orthogonality correction techniques that can lessen image distortions while scanning along different directions.
There is a desire for improved image forming techniques that can combine electronic and graphical elements on a printed article with reduced occurrences of functionality problems and/or visual artifacts.